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fix: HMAC format — match server POST\npath\ntimestamp\nsha256(body) scheme

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- hmac_sign now takes method+path instead of device_id; builds message as
  method\npath\ntimestamp\nhex(sha256(body)) per server verify_device_hmac
- reporter: header renamed X-HMAC-Signature → X-Signature; passes "POST"+path
- test vector regenerated against new message format; timestamp-diff test updated
- .size() → .length() throughout (Arduino String has no size())

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
Peter Woolery
2026-04-14 10:47:13 -07:00
parent 6d41529570
commit 135eb3b46c
4 changed files with 31 additions and 21 deletions
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15
firmware/lib/hmac/hmac.cpp
View File

@@ -35,8 +35,11 @@ static bool sha256(const uint8_t* data, size_t len, uint8_t out[32]) {
return true;
}
HString hmac_sign(const HString& secret_hex, const HString& device_id,
uint32_t timestamp, const HString& body) {
HString hmac_sign(const HString& secret_hex,
const HString& method,
const HString& path,
uint32_t timestamp,
const HString& body) {
// 1. SHA256(body)
uint8_t body_hash[32] = {};
if (!sha256((const uint8_t*)body.c_str(), body.length(), body_hash)) {
@@ -44,10 +47,10 @@ HString hmac_sign(const HString& secret_hex, const HString& device_id,
}
HString body_hash_hex = bytes_to_hex(body_hash, 32);
// 2. Build message
// 2. Build message: method + "\n" + path + "\n" + timestamp + "\n" + sha256(body)
char ts_buf[12];
snprintf(ts_buf, sizeof(ts_buf), "%u", (unsigned)timestamp);
HString message = device_id + ":" + ts_buf + ":" + body_hash_hex;
HString message = method + "\n" + path + "\n" + ts_buf + "\n" + body_hash_hex;
// 3. Decode secret from hex
size_t secret_len = secret_hex.length() / 2;
@@ -59,8 +62,8 @@ HString hmac_sign(const HString& secret_hex, const HString& device_id,
mbedtls_md_context_t ctx;
const mbedtls_md_info_t* info = mbedtls_md_info_from_type(MBEDTLS_MD_SHA256);
mbedtls_md_init(&ctx);
int ret2 = mbedtls_md_setup(&ctx, info, 1);
if (ret2 != 0) { mbedtls_md_free(&ctx); return HString{}; }
int ret = mbedtls_md_setup(&ctx, info, 1);
if (ret != 0) { mbedtls_md_free(&ctx); return HString{}; }
mbedtls_md_hmac_starts(&ctx, secret, secret_len);
mbedtls_md_hmac_update(&ctx, (const uint8_t*)message.c_str(), message.length());
mbedtls_md_hmac_finish(&ctx, hmac_result);

10
firmware/lib/hmac/hmac.h
View File

@@ -11,6 +11,10 @@ using HString = String;
#endif
// Returns lowercase hex-encoded HMAC-SHA256 signature.
// Message signed: device_id + ":" + timestamp_str + ":" + hex(sha256(body))
HString hmac_sign(const HString& secret_hex, const HString& device_id,
uint32_t timestamp, const HString& body);
// Message signed: method + "\n" + path + "\n" + timestamp_str + "\n" + hex(sha256(body))
// Matches server verify_device_hmac format: POST\n{path}\n{timestamp}\n{sha256(body)}
HString hmac_sign(const HString& secret_hex,
const HString& method,
const HString& path,
uint32_t timestamp,
const HString& body);